I guess you see everything in a new way with
permaculture in your mind.
If you want to plant them before identifying I would give them a bit of distance to grow to a full size. Also, can you keep the hawthorn trimmed back pretty easily? I don't know about their characteristics. In the meantime you could plant other shrubs and herbs in the gap to connect them and your hedge if that would make since in your circumstances. If you don't have much space, you could plant them closer and plan to remove one later when the space is getting crowded and you had an idea which you like better, if they were hopefully fruiting by that time. I'm sort of new to this too, especially tree and shrub care, but I've done ok just experimenting and altering my
plans when something doesn't work like I hoped. Good luck!